Application of Quarter Car Model for Assessment of Attenuation Characteristics of Soil at Low Strain

Due to increase in population, industrialisation and a lack of space in the urban areas of Surat city in Gujarat (India), numerous buildings are being constructed in the vicinity of the railway tracks. The perspective is further aggravated by the proposal for a high-speed corridor (≥ 200 kmph) connecting two key Indian cities, Mumbai and Ahmedabad. These structures need to be evaluated for their susceptibility to the dynamic stresses induced by such high-speed locomotives. However, before the assessment of such dynamic stresses, geometrical and material damping properties of the in situ soil must be determined as the stresses induced in the structure also depend on the attenuation characteristics of the subsoil. With the objective to determine attenuation characteristics of the soil due to high-speed trains, the current study uses modelling capabilities of SAP2000 to prepare a vehicle-track-soil interaction model for dynamic analysis of the site in Surat city (India). A quarter car model (lumped mass model) prepared in SAP2000 environment is used to replicate CHR3-type high-speed train. The passage of train over the track structure is represented as a sinusoidal harmonic load. The study establishes that the statistical analysis of the attenuation of the waves is exponentially related to the distance from the source and follows the Bornitz equation. The frequency-independent damping ratio is computed considering near-field and far-field effect of induced vibration in the soil. Finally, the damping ratio and transmissibility are used to derive the critical velocity for the given track near the proposed site.